1. Field of the Invention:
This invention relates generally to slide fasteners and more particularly to a slider therefor.
2. Prior Art:
Numerous types of sliders for opening and closing the slide fasteners have been proposed which are provided with means for locking the slider in position against unintentional movement subject to a force tending to spread or open the fastener. One such locking means was formed on a pull tab attached to and adapted to facilitate movement of the slider body. For slide fasteners, however, having ladder-type or meandering coupling elements in two rows, one on the upper and the other on the lower side of the fastener, the locking means was preferably provided on or in connection with the flange portion of the slider body. A slider with the latter type of locking means was disclosed in U.S. Pat. No. 3,798,714 in which the slider (as shown in FIG. 6) has a pair of locking tabs or projections 100 and 101, one of upper opposed flanges 102 on an upper wing member and the other tab or projection on a corresponding extreme end of one of lower opposed flanges 103 on a lower wing member, the locking tabs 100 and 102 engageable with the heel portions 104 of the coupling elements E respectively on the upper and lower sides of the fastener to prevent spontaneous spreading-apart action of the confronting stringers. Whilst this prior flange-lock slider has its own advantages, it has a drawback in that either one of the pair of locking tabs would fail to lockably engage with the heel portion of the coupling element in the event that the opposed stringers are coupled together with the coupling elements in one row misaligned with respect to those in the other row; that is when the elements on one stringer are interengaged with their counterparts on the other stringer with one element pitch shifted out of position either in the opening or the closing direction of the fastener, or stated otherwise when the coupling elements on the right side are disposed half an element pitch out of alignment with respect to those on the left side as visualized in FIG. 6, in which instance only one of the two locking tabs engages with the heel portion of the element, while the other tab does not because the element to be arrested thereby is displaced half a pitch from the normal position. Thus, such one-sided locking action would not be effective when the fastener is subjected to a lateral pull or force applied to spread its stringers apart.